Infrared thermometers are well known instruments for remotely determining temperature when it is neither possible nor practical to use a direct temperature sensing probe. The infrared light emitted by a target is transmitted to a photosensor which converts the light to electrical signals that are then processed or analyzed for conversion into a visual indication of temperature.
Reference can be made to U.S. Pat. Nos. 2,968,946 of Goldberg et al.; 4,527,869 of Irani et al. and patents and other references cited therein for a more detailed description of such infrared thermometers.
More recently, infrared thermometers have been developed which employ fiber optic cables to transmit light from a remote pickup head containing a fixed focus reimaging lens system to a photosensor of a sensing head which converts the light to electrical signals. These signals are then passed to a processor, or analyzer, which converts the electrical signals to a visual indication of temperature.
These fiber optic infrared thermometers have some disadvantages which hinder their use or interfere with their accuracy. Know remote pickup heads have employed fixed focus lens systems, such that if it is desired to focus on a different target, the entire remote pickup head must be moved relative to the target. This requires relative crude adjustment of the mounting mechanism which holds the remote pickup in place each time it is desired to change focus and renders set up of the instrument difficult. Alternatively, remote pickup heads have been provided which allow for adjustment of the focus but only at the expense of destroying calibration during the adjustment process.
Another problem has been due to the fact that at the sensor head, the light from the end of the fiber optic cable from the target is passed to the photosensor by means of a lens system focused directly on the photosensor. This results in sensitivity and calibration difficulties due to high intensity spots at the end of the fiber optic cable and resultant calibration problems due to improper focusing.
Known fiber optic infrared temperature sensors also lack provision of a selectable field stop, such as an elongated slot shaped field stop. Accordingly, in these sensors the target's selectivity cannot be improved by arranging to have the light from only a selected portion of the entire field of focus impinge on the fiber optic cable and, thus, on the photosensor.